The instant invention relates to polyethylene glycol compounds and a process for making such compounds. More particularly, the instant invention relates to high molecular weight polyethylene glycol compounds having narrow molecular weight distribution and a process for making such compounds. The polyethylene glycol compounds of the instant invention are useful for chemical modification of physiologically active materials, which modified materials are applicable, for example, in drug delivery systems.
Biologically active compounds conjugated with polyoxyalkylenes can provide enhanced biocompatibility for the compound, See, for example, U.S. Pat. No. 5,366,735 and U.S. Pat. No. 6,280,745. A review of this subject by Zalipsky, in Bioconjugate Chem., 1995, 6, p150–165, identified polyethylene glycol as one of the best biocompatible polymers to conjugate with a biologically active compound (such as a drug, a protein, a peptide or an enzyme) to produce a conjugate having improved properties such as compatible solubility characteristics, reduced toxicity, improved surface compatibility, increased circulation time and reduced immunogenicity.
Polyethylene glycol (PEG) is a linear polyoxyalkylene terminated at the ends thereof with hydroxyl groups and generally represented by the formula: HO(CH2CH2O)nH. As discussed by Henmanson in Chapter 15 of Bioconjugate Techniques (1996), monomethoxy polyethylene glycol (mPEG) generally represented by the formula: CH3O(CH2CH2O)nH, is usually used to prepare a polyethylene glycol conjugate with a biologically active compound typically by way of a coupling reaction between an amine group of the biologically active compound and an amine receptive derivative (such as trichloro-s-triazine activated mPEG) formed via the remaining terminal hydroxyl group of the monomethoxy polyethylene glycol.
More recently, so called “second generation” PEGylation chemistry has been developed to, for example, minimize problems of diol impurity contamination of mPEG, to increase the molecular weight of the mPEG and to increase stability of the conjugate, see Roberts et al., Advanced Drug Delivery Reviews 54 (2002) p459–4. U.S. Pat. No. 6,455,639 (herein fully incorporated by reference) described an increased molecular weight mPEG having narrow molecular weight distribution. However, the highest molecular weight disclosed in the '639 patent was 20,861 (weight average molecular weight). It would be a further advance in the art if even higher molecular weight, narrow molecular weight distribution mPEG were discovered along with a processes to produce such a material.